In recent years, electrophotographic photoreceptors have been markedly extending their use in electrophotographic apparatus, such as copying machines, laser beam printers, etc. because of their high-speed and high quality printing performance. Studies have been elaborated on electrophotographic photoreceptors using an organic photoconductive material (hereinafter simply referred to as an organic photoreceptor) for use in these electrophotographic apparatus in view of their advantages in price, productivity, and disposability over those using an inorganic photoconductive material, such as selenium, selenium-tellurium alloys, selenium-arsenic alloys, and cadmium sulfide. In particular, so-called separate function type organic photoreceptors comprising a charge generating layer and a charge transporting layer are excellent in electrophotographic characteristics, such as sensitivity, chargeability, and stability on repeated use, and various proposals on this type of photoreceptors have been made to date, some of which have already been put to practical use. For example, U.S. Pat. No. 4,806,443 discloses a photoreceptor using an arylamine compound as a charge transporting material.
On the other hand, while a development system includes one-component development system and a two-component development system, an electrophotographic system using a microcapsule toner has been studied, in which image fixing is effected by pressure application instead of heat application so as to eliminate excessive energy imposed on the apparatus.
In order to obtain a capsule toner having sufficient pressure fixing properties while maintaining developability (i.e., chargeability), it is necessary to form a capsule structure composed of a core containing an ink comprising a solvent having dispersed therein a pigment and a binder and an outer shell having a charge control function as suggested in JP-A-51-132838, JP-A-58-145964, and JP-A-60-83958 (the term "JP-A" as used herein means an "unexamined published Japanese patent application").
Where a capsule toner having such a structure is used in combination with an organic photoreceptor, a part of a charge control agent present on the shell surface becomes liable to adhere to the organic photoreceptor during long-term use. The adhered substance undergoes denaturation by ozone generated in the copying machine and is rendered electrically conductive. This leads to trouble that the charge of an electrostatic latent image on the photoreceptor is leaked, that is, the image disappears. For this reason, it has been difficult to use a capsule toner in combination with an organic photoreceptor.